In recent years a number of laboratories have sought to explain the biochemial difference between L-asparaginase-sensitive and resistant tumors. The evidence now points to the conclusion that tumors and leukemias that respond to L-asparaginase depend on an exogenous supply of asparagine, whereas the resistant lines have the ability to synthesize their own. The enzyme implicated in this biosynthesis is known as asparagine synthetase (ASase) and its level of activity appears to be considerably higher in murine malignancies than in normal tissue. It now appears that many neoplasms rapidly become resistant to L- asparaginase during clinical use and that there is a similar mechanism of resistance for murine and human tumor tissue, that is, the emergence of ASase activity. This provides a solid rationale for the development of aspartic acid and/or asparagine analogs which could irreversibly inhibit ASase and thus the biosynthesis of asparagine. Our general research plan initially involves the synthesis of a number of analogs related to aspartic acid which constrain such functional groups so as to make them potential irreversible inhibitors of ASase. Secondly, we wish to evaluate these analogs for both reversible and irreversible inhibition of an ASase isolated from Novikoff hepatomas grown in rats. The specific activity of the ASase in the presence of the inhibitor will be determined by the amount of C14- asparagine synthesized and then compared to the control, the ratio of which gives the per cent inhibition. Thirdly, the analogs will be further screened by the CCNSC in both asparaginase-resistant (both natural and variant lines) and sensitive tumors.